1. Field of the Invention
The present invention relates to a wiper controller apparatus of the water drop sensitive type for detecting a condition or amount or volume of water drops adhered to or present upon a surface of a window glass so as to drive the wiper, by using a light emitting element and a light receiving element.
2. Description of Prior Art
A conventional controller apparatus of the water drop sensitive type as disclosed in Japanese Patent Laid-Open No. Hei 2-67945 (1990) is already known. In this prior art document, light means (i.e., light emitting means) and detection means (i.e., light receiving means) are positioned upon an inside surface of a window glass, opposing to each other at a distance, within a wiping area of a wiper wiping an outside surface of the window glass, and the adhesion or presence of the water drops upon the outside surface of the window glass is decided or detected on the basis of a difference between output signal levels generated from the detection means before and after driving of the wiper, so as to drive the wiper. When the output signal of the detection means reaches a certain reference level, the wiper starts to be driven, while it is stopped when the output signal of the detection means falls to be less or lower than aforesaid reference level.
However, with the conventional wiper controller apparatus of the water drop sensitive type, it is impossible to remove or wipe any water drops, present, for example, due to rain, still adhered to or present upon the window glass in such an amount or volume that the output signal of the detection means does not reach the predetermined reference level, in particular after the stopping of rain, since the wiper stop being driven immediately after the output signal of the detection means came to be lower than the reference level. Further, there is also a possibility that any rain drops (water drops) adhered or present upon the window glass without being detected by the detection means may shift or slide down on the window glass (especially, for example, the front windshield of an automobile) into a view region or area other than that that is wiped by the wiper.
In particular in a case where the output signal of the detection means does not reach the reference level, there is still another drawback in that the wiper must be driven by being manually switched on again, since it does not operate automatically.
Further, with the conventional wiper controller apparatus of the water drop sensitive type, the wiper is automatically driven when the output signal from the detection means reaches the predetermined level. Therefore, it has a further drawback in that the wiper can be driven erroneously by the incidence of noise or ambient light from outside, which changes abruptly (in particular, pulse-like light) or that is caused due to the shadow of trees, buildings, tunnels and so on.
Moreover, there is another drawback in that the wiper may be accidentally driven due to electromagnetic noise or radio waves generated by such devices as VICS, mobile phones (car phones), other radio apparatus, or generated from the ignition coil of an automobile's engine, which are incident as noise upon the detection means.